9000

Chapter 5 81

Troubleshooting

Memory Subsystem Latency: The time it takes to move data from

system memory to an I/O device. This time includes the arbitration delay

for the I/O device and for each bus bridge between the system memory

controller and the I/O device.

Arbitration Delay: The time it takes an I/O device or bus bridge to

acquire the I/O bus for data transfer.

Transmit FIFO: A buffer on the FDDI card used to hold data

transferred from system memory to the FDDI card.

The EISA FDDI/9000 and HSC FDDI/9000 products are currently

optimized to achieve the best single card performance. While the current

Transmit Threshold value allows the FDDI products to achieve their

best performance, it also increases the probability of Transmit Underrun

errors. A large number of Transmit Underrun errors (more than 1 out of

every 10,000 packets) can cause a noticeable drop in networking

performance.

Transmit Underrun errors may occur in some HP systems that have

high memory subsystem latencies combined with sufﬁcient bus

contention from competing I/O devices. These errors can be monitored in

two ways:

• Examine the output from netstat -I interface

• Examine the output from fddiif interface

If the number of output errors is high (more than 1 out of every 10,000

packets), then the system is most likely suffering from transmit

underruns on the speciﬁed network interface and corrective action must

be taken to resolve the problem.

EISA FDDI/9000

For the EISA FDDI/9000 product, use the lanadmin -S command to

toggle the use of onboard memory for transmit on or off. (By default, use

of onboard memory for transmit is off.) For example:

lanadmin -S 1 PPA

Note that the value speciﬁed after the -S parameter is not important, as

the command is simply a toggle. After issuing the above command, the

current speed of the interface is echoed; this output may be ignored. You

must then wait at least 5 seconds before attempting to use the speciﬁed

network interface.